Broadway's Gwen Marlowe and Ernest Lane are sweethearts, onstage as stars of Victor Herbert's operetta and offstage as happily marrieds. Then Hollywood beckons, and their fretful stage producer puts the kibosh on any Tinseltown plans by trumping up a romantic triangle that sets the lovebirds feuding. Notable as Metro-Goldwyn-Mayer's first feature film shot in the three-color Technicolor process, the 24-karat Golden Age singing team of